java - 未能延迟初始化角色 : br. com.coderi.adi.model.Usuario.papeis 的集合，无法初始化代理 - 无 session

Question

我正在使用 Java 1.8 处理实体 @OneToMany 和 @ManyToOne 之间的关系以及 Spring-MVC 和 Spring-Data-JPA，但我收到以下错误:

GRAVE: Servlet.service() for servlet [appServlet] in context with path [/adi] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: br.com.coderi.adi.model.Usuario.papeis, could not initialize proxy - no Session] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: br.com.coderi.adi.model.Usuario.papeis, could not initialize proxy - no Session

我可以添加用户 (Usuario) 及其角色 (Papeis)，但执行查询时总是会出现上述错误。

实体Usuario:

@Entity
public class Usuario {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @NotEmpty
    private String nome;

    @NotEmpty
    private String email;

    @NotEmpty
    @Size(min = 2, max = 25)
    @Column(unique = true)
    private String login;

    @NotEmpty
    @Size(min = 6)
    private String senha;

    @Transient
    private String confirmSenha;

    private Boolean status;

    @OneToMany(mappedBy = "usuario")
    private List<Papel> papeis;

    <!-- Getters/Setters... -->
}

实体纸:

@Entity
public class Papel {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @NotEmpty
    private String papel;

    @ManyToOne
    private Usuario usuario;

    <!-- Getters/Setters... -->
}

一个用户(Usuario)可以有多个角色(Papel)，各个角色必须属于一个用户。这是正确的做法吗？

服务:

@Service
public class PapelService {

    @Autowired
    private PapelReposiroty papelRepository;

    public Papel getPapel(Integer id) {
        return papelRepository.findOne(id);
    }

    public Papel adicionar(Papel papel) {
        return papelRepository.save(papel);
    }

    public List<Papel> listarPapeisPorUsuario(Usuario usuario) {
        return papelRepository.findPapelByUsuario(usuario);
    }
}

存储库:

@Repository
public interface PapelReposiroty extends CrudRepository<Papel, Integer> {
    public List<Papel> findPapelByUsuario(Usuario usuario);
}

在我的 Controller 中，当我执行papelService.getPapel(1)时添加用户/角色后，我收到了这个引用的错误。感谢您的帮助!

Ps: The error occurs only when using the methods of relationships.

数据库:

所有堆栈跟踪:

GRAVE: Servlet.service() for servlet [appServlet] in context with path [/adi] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: br.com.coderi.adi.model.Usuario.papeis, could not initialize proxy - no Session] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: br.com.coderi.adi.model.Usuario.papeis, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:579)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:203)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:558)
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:131)
at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:509)
at java.lang.String.valueOf(String.java:2982)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at br.com.coderi.adi.model.Usuario.toString(Usuario.java:113)
at java.lang.String.valueOf(String.java:2982)
at java.lang.StringBuilder.append(StringBuilder.java:131)
at br.com.coderi.adi.model.Papel.toString(Papel.java:66)
at java.lang.String.valueOf(String.java:2982)
at java.io.PrintStream.println(PrintStream.java:821)
at org.apache.tomcat.util.log.SystemLogHandler.println(SystemLogHandler.java:267)
at br.com.coderi.adi.controller.PapelController.adicionarForm(PapelController.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:112)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:169)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:158)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:206)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:121)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:100)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:106)
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:214)
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:177)
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:262)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

Answer 1

How to Enable Lazy Loading in Hibernate

在进一步操作之前，回顾一下默认行为非常重要 使用 hibernate 映射与注释时的延迟加载。

默认行为是立即加载“属性值”并加载 “懒惰地收集”。与您可能记得的相反 之前使用过普通的 Hibernate 2(映射文件)，其中所有引用 (包括集合)默认情况下会立即加载。另请注意 @OneToMany 和 @ManyToMany 关联默认为 LAZY 加载； @OneToOne 和 @ManyToOne 默认为 EAGER 加载。这是 重要的是要记住避免将来陷入任何陷阱。

要显式启用延迟加载，您必须使用“fetch = FetchType.LAZY”在您想要延迟加载的关联上 正在使用 hibernate 注释。

示例用法如下所示:

@OneToMany(mappedBy = "类别", fetch = FetchType.LAZY) 私有(private) 套装产品；另一个平行于的属性 “FetchType.LAZY”是“FetchType.EAGER”，与 LAZY 正好相反 即，当所有者实体是时，它也会加载关联实体 第一次获取。

延迟加载在 Hibernate 中如何工作

Hibernate 可以在您的应用程序上应用延迟加载行为的最简单方法 实体和协会是通过提供代理实现 他们。 Hibernate通过代理来拦截对实体的调用 因为它派生自实体的类。哪里要求的 信息缺失，之前会从数据库加载 控制权被移交给父实体的实现。

请注意，当关联表示为集合时 类，然后是包装器(本质上是集合的代理，而不是 比它包含的实体)被创建并替换 原始集合。当您访问此收集代理时 你在返回的代理集合中得到的不是代理实体； 相反，它们是实际的实体。你不需要施加太大的压力 理解这个概念，因为在运行时它几乎不重要。

您使用@O​​netoMany关系。

我知道要解决。

您使用获取。

您的实体

@Entity
public class Usuario {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @NotEmpty
    private String nome;

    @NotEmpty
    private String email;

    @NotEmpty
    @Size(min = 2, max = 25)
    @Column(unique = true)
    private String login;

    @NotEmpty
    @Size(min = 6)
    private String senha;

    @Transient
    private String confirmSenha;

    private Boolean status;

    @OneToMany(mappedBy = "usuario")
    private List<Papel> papeis;

    <!-- Getters/Setters... -->
}

您搜索“jpa fetch Lazy”。但。 fetch，很多搜索关系。 :)